Shell impregnated catalyst and process for producing a shell impregnated catalyst body

ABSTRACT

The present application relates to a process for producing a catalyst,said process comprising the steps of: providing a carrier and following modifying said carrier by a first impregnation with at least one alkaline earth metal in a first metal precursor solution. The first metal precursor is decomposed to form at least one metal oxide or metal hydroxide thereby obtaining a modified carrier and a second impregnation is carried out by incipient wetness by a second precursor solution comprising at least one metal Me in a second solution. Finally the second precursor is decomposed thereby obtaining a catalyst body having an enrichment of the at least one metal Me in the outer shell of the catalyst body, said at least one metal being present in a concentration having either as an egg-shell profile or a hammock profile.

The invention relates to a catalyst and a process for producing acatalyst for syngas generation.

New catalysts are under constant development as the requirements forefficiency, lifetime and also costs of the catalyst are ever increasing.

For various reasons it may be beneficial to reduce the amount of metalsin the catalyst, for example it may be relevant to minimize the amountof the metal in the catalyst due to environmental considerations. Incatalysts for reactions limited by mass transfer such as steam reformingreactions or catalytic partial oxidation at high temperatures thereactive metal is only needed in the surface zone of a catalyst body,i.e. in such catalyst bodies it may be relevant to have a significantmetal concentration in the surface zone only. This surface concentratedmetal layer also limits unwanted side reactions such as ammoniaproduction in steam reforming of nitrogen rich feedstocks.

On the other hand, however, the requirements to the structural stabilityand lifetime of the catalyst are high as it is critical for loading andrunning the reactors with the catalyst. Due to these requirements tostrength of the carrier, the carrier for e.g. steam reforming catalystsis most often sintered at high temperatures, which reduces thereactivity of the carrier rendering e.g. shell impregnation difficult byknown means.

Thus there is a need for development of new processes for making shellenriched catalysts based on even highly inert carriers.

SUMMARY OF THE INVENTION

In a first aspect of the present process is provided a process whichlimits the consumption of active metal,

In a second aspect of the present process is provided a process whichmaintains the strength of the carrier,

In a second third aspect of the present process is provided a processwhich can be carried out on industrial scale,

These and other advantages are obtained by a process for producing acatalyst, said process comprising the steps of:

-   -   providing a carrier    -   modifying said carrier by a first impregnation with at least one        alkaline earth metal in a first metal precursor solution    -   in a first decomposition, decomposing the first metal precursor        to form at least one alkaline earth metal oxide or hydroxide        thereby obtaining a modified carrier    -   carrying out a second impregnation preferably by incipient        wetness by a precursor comprising at least one metal Me in a        second solution    -   in a second decomposition decomposing the precursor thereby        obtaining a catalyst having an enrichment of the at least one        metal Me in the outer shell of the catalyst body, said at least        one metal being present in a concentration having either an        egg-shell profile or a hammock profile

Thus according to the present method the carriers are first modified byimpregnation by incipient wetness with a solution of a first substancee.g. one or more alkaline earth metals in a metal precursor solutionfollowed by decomposition of the precursor to form an oxide or hydroxidelayer on the carrier.

The hereby deposited oxide/hydroxide layer renders the carrier basic andincreases the surface reactivity. The increased surface reactivityincreases the reactivity towards the second metal Me applied in thesecond impregnation.

The second impregnation is performed by incipient wetness using asolution of a metal precursor. The decomposition of the precursor tometal oxide may be performed. The increase in surface reactivityobtained by modifying the carrier with an alkaline earth metal therebyresults in an enrichment of metal Me in the outer shell of the catalystbody either as an egg-shell profile and/or as a hammock profile.

The first and/or the second impregnation may be repeated one or moretimes in order to achieve a desired metal concentration. For exampleimpregnation with Ni may be carried out two, three or more times inorder to achieve an optimal Ni concentration in the formed shell. Therepeated first and/second impregnation may be carried out with orwithout a following intermediate calcination.

In the present context egg-shell profile means that the metal is presentin a layer in the surface region of the catalyst body. With an egg-shellprofile the metal concentration decreases to zero or substantially zeroin the centre region of the catalyst body. The layer comprising themetal is preferably below 1000 μm, such as below 500 μm.

In the present context hammock profile means that the metal is mainlypresent in a layer in the surface region of the catalyst tablet with ametal concentration which becomes lower but not zero in the centreregion of the catalyst body.

The necessary or preferred shell thickness depends on the specificapplication. The higher the mass transfer limited reaction is, thethinner the shell can be. Thus for instance catalysts for application insecondary reformers may have a thinner shell than catalysts forapplication in primary reformers.

In catalysts to be used at temperatures such as 1000-1200° C. a thinshell (e.g. less than 200 μm) impregnation may be sufficient as thereaction is severely mass transfer restricted.

In catalysts to be used at temperatures such as 700-1000° C. a thickershell (e.g. less than 400 μm) impregnation may be preferred as thereaction is less mass transfer restricted.

The metal-profile of the catalyst body is determined by the applicationof scanning electron microscopy analysis (SEM) using standardless EnergyDispersive X-ray Spectroscopy (EDS)-analysis for chemical composition.The shell thickness is defined as the distance from the outer surface ofthe catalyst body to the position where the metal concentration is 150%of the average metal concentration, as calculated as the averageconcentration from 800 μm and to the centre of the catalyst body. Themetal concentration in the shell is calculated as the average of themeasured metal concentrations in the shell.

The pore volume, porosity and BET surface area is relevant for theresults of the impregnation. Preferably the carrier has a pore volume200-400 ml/kg and/or BET surface area 2.0-50 m²/g, such as 2-25 m²/g.

The BET surface area is determined by single point BET-analysis. Thesample is placed in a U-tube and dried at 300° C. in a flow of heliumfor 8 hours. Hereafter the U-tube with the sample is cooled in a bath ofliquid nitrogen and nitrogen is adsorbed on the sample by exposing thesample to a flow with 30% nitrogen in helium. The nitrogen concentrationin the exit gas from the U-tube containing the sample is determined witha TCD (Thermal Conductivity Detector). When adsorption has come to anequilibrium the cooling bath is removed and a desorption peak isrecorded and integrated. The BET surface area is obtained from theamount of nitrogen desorbed from the sample.

Thereby by the application of the present process it is possible tocontrol the distribution of the metal Me in the catalyst body. I.e. bythe present method is provided a catalyst wherein the active metal isonly or at least predominantly found in the areas of the catalyst tabletwhere the reaction such as steam reforming reaction is kineticallycontrolled during the catalytic process. This means that the activemetal is not or in very limited amount found in the centre of thecarrier i.e. the metal is not or only in limited amount present in areasof the catalyst body where the reaction is thermodynamicallycontrolled/in equilibrium.

By limiting the metal to the shell of the catalyst body secondaryreactions such as ammonia formation are also limited.

Preferred carriers may be alumina spinel such as magnesium aluminaspinel, calcium aluminate (such as CaAl₁₂O₁₉, CaAl₄O₇), zirconia,various alumina such as α- or γ-Al₂O₃ and/or combinations thereof.Preferred are calcium aluminate and/or magnesium alumina spinel as thesecan provide a final catalyst body with a high strength and which is ableto withstand high temperatures and/or high steam pressures of thereforming processes. As mentioned above the first substance applied bythe first precursor solution may be an alkaline earth metal such as Mg,Ca, Sr, and/or Ba.

By the present invention it is possible to create a metal enriched shellon a relatively inert carrier material. Carriers used for steamreforming are most often sintered at high temperatures in order toprovide a sufficient strength of the carrier to withstand the hightemperatures and high steam pressures. However the carrier is not onlymade stronger by sintering but also made less reactive rendering thetask of creating a metal shell non trivial. Carriers for steam reformingmay comprise magnesium alumina spinel or Ca-aluminates as they providehigh thermal stability, high tablet strength and sufficient surface areaafter sintering at very high temperatures. Other typical carriers suchas γ-Al₂O₃ or other transition aluminas provide high catalytic surfacearea but may not be stable under conditions of high temperature and highsteam pressures. γ-Al₂O₃ also require high sintering temperatures inorder to render high tablet strength and good thermal stability underrelevant steam reforming conditions and consequently, upon hightemperature treatments, the γ-Al₂O₃ readily transforms into α-Al₂O₃,which in turn has a very low surface area and is not suitable for somesteam reforming applications. Furthermore, magnesium alumina spinel orCa-aluminates carriers are more basic than alumina-based carriers, thusallowing operation at low steam/carbon ratios without risk of carbondeposition in the catalyst bed, which would significantly decrease thecatalyst lifetime. In other worlds, under relevant steam reformingconditions it might be preferred to use magnesium alumina spinel orCa-aluminates carriers in order to ensure C-free operation. Inconclusion, magnesium alumina spinel or Ca-aluminates carriers orcombinations hereof are preferred over alumina carriers for certainsteam reforming applications.

Preferably the carrier comprises 50-99% MgAl₂O₄ and/or Ca Aluminate,such as at least 80% MgAl₂O₄ and/or Ca Aluminate. E.g. the carriercomprises at least 90% MgAl₂O₄ and/or Ca Aluminate, such as at least 90%MgAl₂O₄ or at least 90% Ca Aluminate. The calcium aluminate may be inthe form of hibonite (CaAl₁₂O₁₉), grossite (CaAl₄O₇) or calciummonoaluminate (CaAl₂O₄), or a combination thereof.

Alkaline earth metals may be chosen as they increase the reactivity ofthe carrier against the metal precursor.

In some embodiments the alkaline earth metal oxide/hydroxideconcentration is 0.5-10 wt % after impregnation. Preferably 1-6 wt %.E.g. 1.5-5 wt %. The applicant has shown that e.g. 1.5 wt % MgO resultsin a clear shell formation. Similarly the applicant has shown that 1.5wt % CaO results in an increased Me concentration in the shell regionand that 3 wt % CaO results in a clear shell formation.

The first decomposition is preferably carried out at a temperature from300-900° C., such as 350-700° C., and/or 400-600° C.

The first decomposition temperature may be selected depending on thefirst precursor solution. For example nitrates may decompose in therange of 350-600° C.

The first decomposition may be carried out in various atmospheresincluding but not limited to air, H₂, N₂ and/or other inerts or reducinggases. The decomposition time may be varied depending on e.g. the firstprecursor solution, decomposition temperature and/or decompositionatmosphere.

The second metal precursor may for example be Me-nitrate, Me-acetate aswell as complexes such as Me-citrate, Me-Ethylenediaminetetraacetic acid(EDTA) or Me-Ethylenediamine (EDA). The metal precursor may be selectedto induce a desired reactivity between the metal precursor and themodified carrier surface.

The impregnated carrier can optionally be dried between the secondimpregnation and the second decomposition as this under some conditionsmay assist the formation of the shell impregnation.

The drying step may be carried out in air at for example at temperatures80-150° C.

The second decomposition is preferably carried out at a temperature from250-600° C., for example 300 or 450° C.

The second decomposition may be carried out in air, H₂, N₂ or otheratmosphere preferably for 0.5-5 hours, such as 1-4 hours.

The second decomposition may depending on applied decompositionatmosphere decompose the specific metal precursor into a metal oxide, ametal or a combination hereof.

E.g. the metal may be present as NiO or Rh₂O₃ after decomposition inair. If reduced and/or during operation under reforming conditions themetals may be present at least partly in reduced form as Ni, Rh, Ru etc.

The resulting catalyst body may preferably be used in steam reforming,primary and/or secondary reforming and/or in catalytic partial oxidationof methane.

The formed catalyst has a core section and a shell section. The coresection comprises the carrier material impregnated with the alkali earthmetal oxide or hydroxide. The shell section comprises the carriermaterial impregnated with the alkali earth metal oxide or hydroxide aswell as the metal Me.

The thickness of the shell section may vary but may for example be from5-1000, such as 10-800 μm or 30-700 μm or below 500 μm but above 5 μm.

The shell thickness are calculated as the distance from the outersurface of the catalyst body to the position where the metalconcentration is 150% of the average metal concentration, as calculatedas the average concentration from 800 μm and to the centre of thecatalyst body.

In other words the shell thickness may be defined as the distance fromthe outer surface of the catalyst to the points where the metal Meconcentration is 150% of the average of the Me concentration in thecentre core section.

Where the average concentration in the centre section is at or below theminimum measurement threshold approximately 0.5 wt % (by EDS) the shellmay be defined as to start where the metal concentration is 1.5 times0.5 wt %.

In many embodiments it may be desired that the majority of the metal Meis found in a relatively small part of the catalyst. For example atleast 90% of the metal Me such as Ni, Ru and/or Rh is found in the shell(e.g. within an outer layer of up to 500 μm) as measured by EDS or WDS.

The relative shell thickness may vary but in several embodiments theshell thickness is 50% or less of the catalyst radius (average distancefrom centre to outer surface), such as less than 30% or less than 20% orless than 10% of the radius.

A preferred catalyst may comprise a core section and a shell section,wherein

-   the carrier is magnesium alumina spinel and/or calcium aluminates    and/or where the alkaline earth metal oxide and/or alkaline earth    metal hydroxide is MgO, Mg(OH)₂, CaO and/or Ca(OH)₂, and-   the shell section comprises magnesium alumina spinel and/or calcium    aluminates and MgO, Mg(OH)₂, CaO and/or Ca(OH)₂ and at least one    metal Me.

Depending on the intended use, the metal Me is Ni, Ru and/or Rh.

The concentration of alkaline earth metal oxide and/or alkaline earthmetal hydroxide such as MgO, Mg(OH)₂, CaO and/or Ca(OH)₂ in the coresection is 0.5-10 wt %, such as 1-5 wt %. The concentration of alkalineearth metal oxide and/or alkaline earth metal hydroxide may be varied inorder to achieve a desired shell thickness. For example 2, 3, 4, 5, 6 wt% may result in a sharp a relatively narrow shell which may be desirablee.g. if the catalyst is to be used at high reaction temperatures such as700-1400° C.

The average concentration of Me in the shell may in some embodiments be<20 wt %, <15 wt % such as 1-15 wt %, <10 wt % such as 0.75-10 wt % or1.5-10 wt %.

In catalyst according to the present application the Me concentration islower in the center than in the shell. For example the average Meconcentration in the center region may be 50% or less (such as 33% orless, 25% or less or 10% or less) of the average Me concentration in theshell.

Preferably the Me concentration is <5 wt % or in some cases morepreferably <2 wt % in the center. In some embodiments the Meconcentration is substantially 0 wt % in the center of the catalyst.

The catalyst may be a cylinder, sphere, elongated hexagonal etc. Varioustablet shapes and sizes may be used for the catalyst according to thepresent application.

The catalyst may have a massive body or a body with one or moreindentation and/or through-going holes.

The catalyst may in various embodiments have a diameter (or averagecross section if not circular) of 3-100 mm, preferably 5-50 mm, such as10-35 mm which is relevant for many industrial catalysts.

Thus, according to the present method is provided a catalyst, e.g. asteam reforming catalyst, which is very strong and thereby able tosurvive under the often very harsh conditions present in catalyticprocesses. For example under steam reforming, in steam reformers wherevery high temperatures and high water partial pressures are applied.

Thus an advantage of the new synthesis method is that by impregnatingthe carrier with an alkaline-earth metal the carriers basicity and/orreactivity is increased without changing the strength or the structuralintegrity of the catalyst body. This changes the carriers affinity forreaction with a particular metal -precursor on a subsequent secondimpregnation. Thereby by the application of the present process it ispossible to control the metal e.g. Ni-distribution in the catalyst body.

EXAMPLES AND DETAILED DESCRIPTION OF THE INVENTION

In the below various examples are provided. The examples are to beregarded as exemplary in order to illustrate and elaborate on steps ofthe method and catalyst body product. The examples are not to beconstrued as limiting to the invention.

Example I

Carrier:

A magnesium alumina spinel carrier containing 92 wt % MgAl₂O₄ and 8 wt %Al₂O₃ with a pore volume of 260 ml/kg, a porosity of 46% and a BETsurface area of 20 m2/g.

Impregnation of the carrier with an alkaline earth metal: The carrier isimpregnated by incipient wetness with a Ca(NO₃)₂ solution at roomtemperature for half an hour to obtain 3 wt % Ca0 on the carrier. Afterimpregnation the calcium nitrate is decomposed at 550° C.

Impregnation of the modified carrier with a nickel metal precursor:

The carrier is impregnated by incipient wetness at room temperature witha nickel nitrate solution containing 7 wt % Ni. After impregnation thenickel nitrate is decomposed at 450° C.

Example II

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with an alkaline earth metal: The carrier isimpregnated by incipient wetness at room temperature with a Ca(NO₃)₂solution as described in example I, Carrier.

Impregnation of the modified carrier with a nickel metal precursor:

The carrier is impregnated by incipient wetness at room temperature witha 0.6 M (M stands for molar concentration and this abbreviate is usedthroughout the document) nickel acetate solution. After impregnation thenickel acetate is decomposed at 450° C.

Example III

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with an alkaline earth metal: The carrier isimpregnated by incipient wetness with a Ca(NO₃)₂ solution as describedin example I carrier Impregnation of the modified carrier with a nickelmetal precursor:

The carrier is impregnated by incipient wetness at 80° C. with a nickelcitrate solution containing 9 wt % Ni. The solution was prepared bydissolving 7.6 g nickelhydroxycarbonate containing 42% Ni and 11.4 gcitric acid in 15 ml water at 80° C. After impregnation the nickelcitrate is decomposed at 450° C.

Example IV

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with an alkaline earth metal: The carrier isimpregnated by incipient wetness with a Mg(NO₃)₂ solution to obtain 3 wt% MgO on the carrier. After impregnation the magnesium nitrate isdecomposed at 350° C.

Impregnation of the modified carrier with a nickel metal precursor:

The carrier is impregnated by incipient wetness with a nickel citratesolution as described in example III. After impregnation the nickelcitrate is decomposed at 450° C.

Example V

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with an alkaline earth metal: The carrier isimpregnated by incipient wetness with a Mg(NO₃)₂ solution as describedin example IV.

Impregnation of the modified carrier with a nickel metal precursor:

The carrier is impregnated by incipient wetness at 40° C. for half anhour with a 1.2 M nickel EDTA solution. The Ni-EDTA solution is preparedby dissolving 11.2 g EDTA in 30 ml concentrated ammonia solution at 40°C. and adding 11.2 g nickel nitrate. After impregnation the nickel EDTAis decomposed at 450° C.

Example VI

Carrier:

A calciumaluminate carrier containing 53 wt % CaAl₄O₇, 33 wt %CaAl₁₂O₁₉, 13 wt % Al₂O₃ and 1 wt % MgAl₂O₄ with a pore volume of 280ml/kg, a porosity of 46% and a BET surface area of 2 m²/g.

Impregnation of the carrier with an alkaline earth metal: The carrier isimpregnated by incipient wetness with an Ca(NO₃)₂ solution as describedin example I.

Impregnation of the modified carrier with a nickel metal precursor:

The carrier is impregnated by incipient wetness with a nickel citratesolution as described in example III. After impregnation the nickelcitrate is decomposed at 450° C.

Example VII

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with an alkaline earth metal:

The carrier is impregnated by incipient wetness with a Mg(NO₃)₂ solutionas described in example IV.

Impregnation of the modified carrier with a nickel metal precursor:

The carrier is impregnated by incipient wetness with a nickel citratesolution as described in example III. After impregnation the nickelcitrate is decomposed at 450° C.

Example VIII

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with an alkaline earth metal: The carrier isimpregnated by incipient wetness with a Mg(NO₃)₂ solution as describedin example IV.

Impregnation of the modified carrier with a nickel metal precursor:

The carrier is impregnated by incipient wetness at room temperature witha 0.5 M nickel ethylenediamine solution (nickel-EDA). The solution wasprepared by dissolving 4.4 g of nickel-nitrate in 30 ml demineralizedwater and adding 1.8 g of ethylenediamine. After impregnation the nickelEDA is decomposed at 450° C.

Example IX

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with an alkaline earth metal: The carrier isimpregnated by incipient wetness with a Mg(NO₃)₂ solution as describedin example IV.

Impregnation of the carrier with a Ru metal precursor: The carrier isimpregnated by incipient wetness with a solution ofrutheniumnitrosylnitrate to obtain 0.5 wt % Ru on the carrier. Theimpregnation liquor was prepared by diluting with water a commercialavailable solution containing 8.2% rutheniumnitrosylnitrate. Afterimpregnation the catalyst is dried at 80° C. for one hour.

Example X

Carrier: A carrier containing magnesium alumina spinel (MgAl₂O₄) andα-alumina with a pore volume of 406 ml/kg, a porosity of 62% and a BETsurface area of 4 m²/g

Impregnation of the carrier with an alkaline earth metal: The carrier isimpregnated by incipient wetness with a 3.5 M Mg(NO₃)₂ solution.Calcined for two hours at 550° C.

Impregnation of the carrier with a metal precursor solution:

Impregnation for 6 minutes by incipient wetness with a solutioncontaining 0.26 M Rh (as Rh(NO₂)₂), 0.4 M Al (as Al(NO₂)₂) and 2.8 M Mg(as Mg(NO₃)₂), where the pH of the solution was adjusted to about 3-3.5with aqueous ammonia. Final calcination at 750° C. for 2 hours.

Example XI Comparative Example

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with a nickel metal precursor: The carrieris impregnated by incipient wetness at room temperature with a 0.6 Mnickel acetate solution. After impregnation the nickel acetate isdecomposed at 450° C. The impregnation and calcination is repeated twotimes.

Example XII Comparative Example

Carrier: A carrier as described in example I is used. Impregnation ofthe carrier with a nickel metal precursor: The carrier is impregnatedwith a nickel citrate solution as described in example III. Theimpregnation and calcination was repeated one time.

Example XIII Comparative Example

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with a nickel metal precursor: The carrieris impregnated by incipient wetness at 80° C. with a nickel nitratesolution containing 9 wt % Ni. After impregnation the nickel nitrate isdecomposed at 450° C. The impregnation and calcination was repeated onetime more.

Example XIV

Carrier: A carrier as described in example VI is used.

Impregnation of the carrier with a nickel metal precursor: The carrieris impregnated with a nickel citrate solution according to the proceduredescribed in example XIII.

Example XV

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with a Ru metal precursor: The carrier isimpregnated according to the procedure given in example IX.

Example XVI

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with an alkaline earth metal: The carrierfrom example I is impregnated by incipient wetness with a Ca(NO₃)₂solution at room temperature for half an hour to obtain 1.5 wt % CaO onthe carrier. After impregnation the calcium nitrate is decomposed at550° C.

Impregnation of the modified carrier with a nickel metal precursor:

The carrier is impregnated by incipient wetness with a nickel citratesolution as described in example III. After impregnation the nickelcitrate is decomposed at 450° C.

Example XVII

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with an alkaline earth metal: The carrierfrom example I is impregnated by incipient wetness with a Ca(NO₃)₂solution at room temperature for half an hour to obtain 5.0 wt % CaO onthe carrier. After impregnation the calcium nitrate is decomposed at550° C.

Impregnation of the modified carrier with a nickel metal precursor:

The carrier is impregnated by incipient wetness with a nickel citratesolution as described in example III. After impregnation the nickelcitrate is decomposed at 450° C.

Example XVIII

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with an alkaline earth metal: The carrier isimpregnated by incipient wetness with a Mg(NO₃)₂ solution to obtain 1.5wt % MgO on the carrier. After impregnation the magnesium nitrate isdecomposed at 350° C.

Impregnation of the modified carrier with a nickel metal precursor:

The carrier is impregnated by incipient wetness with a nickel citratesolution as described in example III. After impregnation the nickelcitrate is decomposed at 450° C.

Example XIX

Carrier: A carrier as described in example I is used.

Impregnation of the carrier with an alkaline earth metal: The carrier isimpregnated by incipient wetness with a Mg(NO₃)₂ solution to obtain 4.5wt % MgO on the carrier. After impregnation the magnesium nitrate isdecomposed at 350° C.

Impregnation of the modified carrier with a nickel metal precursor:

The carrier is impregnated by incipient wetness with a nickel citratesolution as described in example III. After impregnation the nickelcitrate is decomposed at 450° C.

The metal-profile of the catalyst tablets has been examined by theapplicant by scanning electron microscopy analysis (SEM) usingstandardless Energy Dispersive X-ray spectroscopy (EDS)-analysis forchemical analysis. Prior to analysis the catalysts were reduced inhydrogen and pasivated in clean air (O₂/N₂ mix with low O₂ content) atroom temperature. Ni, Rh based catalysts were reduced at 525° C. andRu-based catalysts at 350° C. The samples were cleaved into half tablet,which were embedded in epoxy and polished to obtain a flat surface. Theembedded samples were re-embedded; ground and polished (with waterpresent). To prevent charging during the SEM analysis, the samples werecoated with carbon. The obtained profiles are displayed in FIGS. 1-4.The profile type and shell thickness are summarized in Table 1 and 2.The shell thickness is calculated as the distance from the outer surfaceof the catalyst body to the position where the metal concentration is150% of the average metal concentration, as calculated as the averageconcentration from 800 μm and to the centre of the catalyst body.

The metal concentration in the shell is calculated as the average of themeasured metal concentrations in the shell.

The maximum metal concentration in the shell is the highest metalconcentration measured in the shell, which is typically very close tothe outer surface.

Hammock-shell in table 1 means that there is a shell formation but themetal concentration does not decrease to zero or substantially zero (orbelow the minimum measurement threshold 0.5 wt %) in the centre.

For the Ru-containing samples wavelength dispersive X-ray spectroscopy(WDS) was used to determine the Ru concentration profiles. With thismethod Ru standards are used to enable an accurate determination of theRu concentration which is lower. Hence, WDS has a lower detection limitthan EDS.

TABLE 1 Metal profile type and concentration of metal in the catalystbody Maximum Metal metal Profile Concentration concentrationtype/thickness in shell in shell Example Carrier Precursor μm wt % wt %I MgAl₂O₄/CaO Ni-nitrate shell - 742 4 5 II MgAl₂O₄/CaO Ni-acetateshell - 176 1 1.5 III MgAl₂O₄/CaO Ni-citrate shell - 155 4 7 IVMgAl₂O₄/MgO Ni-citrate shell - 46 7 8 V MgAl₂O₄/MgO Ni-EDTA Hammock 3 4Shell-376 VI CaAluminate/ Ni-citrate shell - 447 4 6 CaO VIICaAluminate/ Ni-citrate hammock 8 11 MgO shell-103 VIII MgAl₂O₄/MgONi-EDA hammock 2 2.2 shell - 90 IX MgAl₂O₄/MgO Ru(NO)(NO₃)₃ shell-90 22.6 X MgAl₂O₄/MgO Rh-nitrate shell-200 2 3.9

TABLE 2 Comparative example: Metal profile type and concentration ofmetal in the catalyst body Metal Exam- Profile Concentration ple CarrierPrecursor type/thickness wt % XI MgAl₂O₄ Ni-acetate homogeneous 3 XIIMgAl₂O₄ Ni-citrate homogeneous 4-11 XIII MgAl₂O₄ Ni-nitrate Homogeneous8 XIV CaAluminate Ni-citrate Homogeneous 12 XV MgAl₂O₄ Ru(NO)(NO₃)₃homogeneous 1

FIG. 1. Nickel concentration profiles measured by EDS analysis along thecross-section of the catalyst body for examples I-VIII. The line scanswere measured from the outer surface of the catalyst body and inwards.There is an uncertainty of +/−30 μm on the measured position. 1000μm hasbeen used as the center for these plots and related table values.

FIG. 2. Nickel concentration profiles measured by EDS analysis along thecross-section of the catalyst body for examples XI-XIV. The line scanswere measured from the outer surface of the catalyst body and inwards.There is an uncertainty of +/−100 μm on the measured position.

FIG. 3. Ruthenium concentration profiles measured by wavelengthdispersive X-ray spectroscopy (WDS) analysis along the cross-section ofthe catalyst body for examples IX and XV. The line scans were measuredfrom the outer surface of the catalyst body inwards.

FIG. 4. Rhodium concentration profiles measured by EDS analysis alongthe cross-section of the catalyst body for example X. The line scanswere measured from the outer surface of the catalyst body and inwards.

FIG. 5. Nickel concentration profiles measured by EDS analysis along thecross-section of the catalyst body for examples I-XVI-XVII. The linescans were measured from the outer surface of the catalyst body inwards.1.5 wt % CaO results in an increased Ni concentration in the shellregion and a clear and sharp shell formation at both 3 and 5 wt % CaO.It appears that 5wt % results in a slightly sharper shell than 3 wt %.

FIG. 6. Nickel concentration profiles measured by EDS analysis along thecross-section of the catalyst body for examples IV-XVIII-XIX. The linescans were measured from the outer surface of the catalyst body inwards.

1.5 wt % MgO results in a clear shell region and a clear and sharp shellformation is also registered at both 3 and 4.5 wt % MgO. It appears that3wt % results in a slightly sharper shell than 5wt %.

FIG. 7. Optical images of 4 mm impregnated cylinders cut in the middlethrough the cross-section. The images reveal the areas containing nickel(grey or black) and the areas not containing nickel (white). For theseexamples, the same spinel and Ca-aluminate carriers were used asstarting point as described in examples I and VI but shaped (pressed)into 4 mm cylinders. The cylinders where first pre-modified withdifferent amounts of either CaO or MgO, as described in examples I andIV, and subsequently impregnated with either Ni nitrate, Ni acetate orNi citrate solutions, as described in examples I, II and III. Thedetails on the carrier, wt % of the pre-modifier and the nickelprecursor used are described in the following:

-   -   (A) Magnesium alumina spinel carrier without pre-modifier        impregnated with Ni nitrate sol.    -   (B) Calcium aluminate carrier without pre-modifier impregnated        with Ni nitrate sol.    -   (C) Magnesium alumina spinel carrier pre-modified with 4.5 wt %        MgO and impregnated with Ni nitrate sol.    -   (D) Calcium aluminate carrier pre-modified with 4.5 wt % MgO and        impregnated with Ni nitrate sol.    -   (E) Calcium aluminate carrier pre-modified with 1.5 wt % MgO and        impregnated with Ni acetate sol.    -   (F) Magnesium alumina spinel carrier pre-modified with 3.0 wt %        CaO and impregnated with Ni citrate sol.    -   (G) Magnesium alumina spinel carrier pre-modified with 4.5 wt %        MgO and impregnated with Ni citrate sol.    -   (H) Magnesium alumina spinel carrier pre-modified with 4.5 wt %        MgO and impregnated with Ni acetate sol.    -   (I) Magnesium alumina spinel carrier pre-modified with 5.0 wt %        CaO and impregnated with Ni acetate sol.    -   (J) Calcium aluminate carrier pre-modified with 4.5 wt % MgO and        impregnated with Ni acetate sol.

1. A process for producing a catalyst, said process comprising the stepsof: providing a carrier modifying said carrier by a first impregnationwith at least one alkaline earth metal in a first metal precursorsolution decomposing the first metal precursor to form at least onemetal oxide or metal hydroxide thereby obtaining a modified carriercarrying out a second impregnation by incipient wetness by a secondprecursor solution comprising at least one metal Me in a second solutiondecomposing the second precursor thereby obtaining a catalyst bodyhaving an enrichment of the at least one metal Me in the outer shell ofthe catalyst body, said at least one metal being present in aconcentration having either an egg-shell profile and/or a hammockprofile.
 2. A process according to claim 1 wherein the carrier isalumina spinel and/or calcium aluminate.
 3. Process according to claim1, wherein carrier has a pore volume 200-400 ml/kg, and/or BET surfacearea 2-50 m²/g.
 4. Process according to claim 1, comprising repeatingthe second impregnation one or more times.
 5. A process according toclaim 1, wherein the first precursor solution is a nitrate, carbonate orhydroxide of the alkaline earth metals.
 6. A process according to claim1, wherein the first decomposition is carried out at 350-550° C.
 7. Aprocess according to claim 1, wherein the alkaline earth metal is takenfrom the group of Mg, Ca, Sr and/or Ba.
 8. A process according to claim1, wherein the alkaline, earth metal concentration is 0.5-10 wt % afterimpregnation.
 9. A process according to claim 1, wherein the secondsolvent is a metal Me precursor in the form of nitrate, acetate,citrate, EDTA and/or EDA.
 10. A process according to claim 1, whereinthe metal Me is Ni, Ru, Rh, Ir, Pd and/or Pt.
 11. A process according toclaim 1, wherein the metal Me is Ni, Ru and/or Rh.
 12. A processaccording to claim 1, wherein the impregnated carrier is dried betweenthe second impregnation and the second decomposition.
 13. A processaccording to claim 1, wherein the second decomposition is carried out at350-600° C.
 14. A catalyst produced by the process according to claim 1.15. A catalyst comprising a core section and a shell section, whereinthe core section comprises a carrier, preferably from alumina spineland/or calcium aluminates, and at least one alkaline earth metal oxideand/or alkaline earth metal hydroxide the shell section comprises thecarrier, preferably alumina spinel and/or calcium aluminates, and atleast one alkaline earth metal oxide and/or alkaline earth metalhydroxide and at least one metal Me.
 16. A catalyst according to claim15, comprising a core section and a shell section, wherein the carrieris alumina spinel and/or calcium aluminates and/or where the alkalineearth metal oxide and/or alkaline earth metal hydroxide is MgO, Mg(OH)₂,CaO and/or Ca(OH)₂, and the shell section comprises alumina spineland/or calcium aluminates and MgO, Mg(OH)₂, CaO and/or Ca(OH)₂ and atleast one metal Me.
 17. Catalyst according to claim 15, wherein themetal Me is Ni, Ru and/or Rh.
 18. Catalyst according to claim 15,wherein the concentration of alkaline earth metal oxide and/or alkalineearth metal hydroxide such as MgO, Mg(OH)₂, CaO and/or Ca(OH)₂ in thecore section is 0.5-10 wt %.
 19. Catalyst according to claim 15, whereinthe concentration of Me in the shell is <20 wt % wt %.
 20. Catalystaccording to claim 15, wherein the pore volume is 200-500 ml/kg and/orBET surface area is 2-50 m²/g.
 21. Catalyst according to claim 15,wherein the shell thickness is 10-1000 μm.
 22. Catalyst according toclaim 15, wherein the shell thickness is 40-500 μm.
 23. Catalystaccording to claim 15, wherein the shell thickness is 50-300 μm. 24.Catalyst according to claim 15, having a radius of 5-100 mm. 25.Catalyst according to claim 15, having a spherical, cylindrical, orother shape.
 26. Catalyst according to claim 15, having a body with oneor more indentation and/or through-going holes.
 27. A catalyst obtainedaccording to the process of claim 1, the catalyst comprising a coresection and a shell section, wherein the core section comprises acarrier from alumina spinel and/or calcium aluminates, and at least onealkaline earth metal oxide and/or alkaline earth metal hydroxide, theshell section comprises the carrier, preferably alumina spinel and/orcalcium aluminates, and at least one alkaline earth metal oxide and/oralkaline earth metal hydroxide and at least one metal Me.
 28. Processfor producing a syngas, said process comprising at least one reformingstep of contacting a feed stream with a catalyst according to claim 1and wherein the reforming step comprises steam reforming, primaryreforming, secondary reforming auto thermal reforming and/or partialoxidation.
 29. Use of a catalyst according to claim 1, for steamreforming, primary reforming, secondary reforming, autothermal reformingand/or partial oxidation.
 30. A reformer comprising a catalyst accordingto claim 1.